Topographical stereoscope



Jan. 10, 133. A. BARR TOPOGRAPHICAL STEREOSCOPE Filed June 2, 1930 Jays.

l A T E L PATENT OFFIC ABCHIBALD BARB, OF .NNIBfiLAND, GLASGOW,SCOTLAND, ASSIGNOR TO BARB AND STRO'UD, LIMITED, F GLASGOW, SCOTLANDTOPOGBAPHICAL STEREQSCOPE Application filed June 2, 1930, Serial No.458,956, and in Great Britain June 14, 1929.

This invention refers to topographical stereoscopes designed for work ofthe same general character as that for which the instrument described inspecification of United 5 States Patent No. 1,743,952, granted to Barrand Stroud, Limited, was devised, bu t 1t 15 not intended to be soportable as that instrument is, in that it refers to instruments havinga rigid base on which two tables are mounted to carry two photographs,thetables being movable rotationally, and the invention relates toimprovements in or connected with base components for such instruments,comprising the use of movable grid plates which are placeable over thephotographs; the particular object of the invention being the provisionof improved mechanical means for effecting the necessary ad ustments andmeans for making measurements of the rela- 530 tive positions of detailson the photographs, and generally for providing a topographlcalstereoscope of a simple kind available for accurate work.

According to this invention the two grid plates, one placed over each ofthe photographs, are movable longitudinally together and one is movablelongitudinally relatively to the other.

An example of construction will now be described. The front edge of thebase plate (which may be of cast metal) is formed to serve as alongitudinal guide. The reflector elements of the instrument may besimilar to those described and illustrated in specification of thepatent referred to, but inthis case they need not be made foldable.These reflector elements are carried from standards extending upwardsfrom the base plate preferably in the central part of the length. The

tables for carrying the photographs are metal plates of disc formationand may be circular, rectangular, or polygonal in out line. They maycarry surface insertions composed, say, of wood, into which drawing pinsmay be pressed for holding the photographs in position, or thephotographs may be attached by means of adhesive material, or they maybe held by clips provided on or in connection with the tables.

Each table has at its centre on the under side an axial projection aboutwhich it is r0- tatable. For rotation each table is provided with atoothed segment concentric with its axis and a shaft with a worm meshingwith the segment is provided with a working head projecting from the endof the platform. The grid plates are carried from a tubular piece whichextends along the baseplate behind the photograph tables and above thelevel of the top of the base. Screws are provided for longitudinalmotion of the grids, the gear being so designed that the screw which hasits working head, say, at the left hand end of the tube moves the gridplates equally to right or left while another screw having its head atthe other end of the tube moves one of the grids relatively to theother.

The grid plates are carried from the tubular piece referred to by doublehinging in such a manner that the grid plates may lie flat upon thephotographs whether thick photographs or thin ones are placed on thetables.

The photographs should be placed on the tables with the principal pointof each photograph lying exactly over the centre of rotation of itstable. This point may be indicated when the photograph is lying on thetable, by any suitable means. For example, a strip of transparentcelluloid may be arranged to lie over the photograph and to be held in adefinite position relatively to the table and have marked upon it thecentre of rotation of the table, so that the principal point of thephotograph may be brought under the point so indicated; or a jig may beprovided consisting of a triangular frame, provided at two of itscorners with feet adaptedto fit respectively into a conical recess andan angled groove near the edge of the table surface, while the thirdcorner is provided with a projecting needle; the disposition of theparts being such that, when the feet are in the recesses, the needlefits into a small hole drilled at the centre of the table. If the needlebe put through the photograph at its principal point and the feet arethen placed in the hole and slot. the needle point will enter the holein the centre of the table; the photograph may then be rotated about theneedle point approximately into the reuired orientation and fixed to thetable. he jig may then be removed and the orientation finally adjustedby rotation of the table in accordance with observations made when thetwo photographs have thus been approximately adjusted.

For measurement of the X and Y coordinates of any points on thephotographs, that is, the co-ordinates parallel to the plane of thephotographs, say with the principal point as zero of co-ordinates, adevice of somewhat T-square form may be used. The head of the T-squareis adapted to slide longitudinally on the base plate and is providedwith an index or a Vernier to read on a scale carried on the base late.One such scale is provided for each p otograph and it may be ad'ustablelongitudinally on the base plate. After the photographs have beenadjusted rotationally relatively to each other and comfortable fusionobtained by the particular observer using the instrument by such meansas are provided the T-square may be placed over the photograph on whichmeasurements are to be made and adjusted so that theedge of the blade ofthe T-s uare lies over the principal point of the p iotograph; the scaleis then adjusted if necessary on the base plate so that it reads zero atthe index or Vernier rovided on the head of the T-square. The blade ofthe T-square is graduated in each direction froma centralpoint whichcoincides with the principal point. If, now, the T-square is moved alongthe base till its edge intersects a point whose coordinates arerequired, the X co-ordinate may be read from the scale carried on thebase, and the Y co-ordinate read on the scale of the blade of theT-square.

After the photographs have been correctly adjusted for orientation andotherwise, the air base line may be accurately drawn on the photographsby aid of a straight edge laid over the photographs and brought intocontact with two stops fixed to the base plate.

An example of construction will now be described with reference to theaccompanyingrdrawing, in which z igure 1 is a front elevation, Figure 2is a broken plan partly in section, Figure 3 is an end view, and Figure4 is a plan showing a T-square.

The construction illustrated comprises a base A, two tables B B two gridplates C G .a face piece D, two eye mirrors E E and two ob'ect mirrors FF The base A is formed with a straight front edge 2, and near the edge 2it is formed to receive two scales 3 3 each of which, for adjustment maybe movable longitudinally, that is movable parallel to the front edge 2,the scales being, for example, slidable in a channel 18 parallel to theedge 2 and being frictionally maintained in the positions to which theyare set. The tables B B which are shown circular, are mounted on thebase A and are rotatable each about its vertical axis. The table B isrotatable by means of a head 4 which operates a worm 5 meshing with atoothed segment 6 movable with the table, and the table B is rotatablesimilarly b means of a head 4 Each of the grid plates C C is adapted tolie u on a photogra h placed upon its associate table. The gri plates,which are of glass, have on their under surfaces a set of lines forminga grid or some other set of marks, those on the two glass platescorresponding to each other. The two grid plates are connected with thebase A by a system of double hinging to permit each plate to lie fiatupon the photograph on its table, irrespective of the thickness of thephotograph. In the example shown each grid plate is mounted in a framewhich is pivoted at 7 to arms 8, the axis of the pivot at 7 is parallelwith the front edge 2 of the base A, and the. arms 8 are movableangularly about a sleeve 9 the axis of which is also parallel with thefront edge 2. The grid plates C C are movable together lonitudmally andprovision is made for moving ongitudinally one of the rid platesrelatively to the other. For t is purpose, the arms 8 for the rid platesC C, extend from two yokes, 9. yo e 8 for the arms of plate C, and ayoke 8 for the arms of plate C, and each yoke is bored to fit onto thecylindrical sleeve 9 which extends longitudinally at the back of thetable. The sleeve 9 is rotatable in bearings 10 which extend from thebase A, and the sleeve 9 and with it the yokes 8 8, are movablelongitudinally by means of a screwed spindle 12 which is rotatable by ahead 12. Endwise movement of the yoke 8 relatively to the sleeve 9 isprevented by collar engagement, and endwise movement of the yoke 8relatively to the sleeve 9 is normally prevented by a spindle 13 whichis threaded to screw into a part of the yoke 8 and relatively to thesleeve 9 the spindle 13 is prevented by collar engagement from movementendwise. Spindle 13 is rotatable by a head 13. Thus, by rotating head 13the grid plate C is moved longitudinally relatively to the grid plate C,and by rotating head 12 the two grid plates C C are .moved similarlylongitudinally. The face plate D is formed with two apertures for theeyes of the observer to look through, and, since in the exampleillustrated the tables are not movable longitudinally nearer to orfurther apart, the eye mirrors E E are movable angularly abouttransverse axes at 14 to obtain fusion stereoscopically. The straightfront edge 2 serves as a guide for the head of a device of substantiallyT-square formation designated H, referred to in the general descriptionof the invention, and having graduations 17 on its blade.

Pins 15, see Figure 2, may be provided projecting upwards from the baseA, against which a straight edge may be placed to guide a pencil or thelike in marking the air base on each of the photographs.

The marks, say grid lines on the under sides of the two grid platesbeing alike, when seen-stereoscopically, appear as a fiat level netstretched over the field of view. When the grid plates 0, C are movedtowards or from each other, by rotation of the head 13, the net appearsto move towards or from the observer, that is, to rise or to fall, andits apparent distance may thus be made to correspond to the apparentheight of any point on the landscape viewed. Thus, by relativelongitudinal-movement of the grid plates, the relative heights ofvarious objects in the landscape may be judged and the form and positionof contour lines on the ground may be observed. When the direction andthe position of a contour line at any part of the landscape have beenseen, one of the grid plates, say C, may be hinged up so that a pencilmay be used to mark on the photograph the contour line referred to. Theposition of the grid plates C, C in any settmg relative to thephotographs, can be determined by reference to the scales 3, 3Longitudinal movement of the grid plates together, by rotation of thehead 12, causes the met to be displaced longitudinally relatively ingthe grid plates to the base plate, means for movmg said grid plateslongitudinally parallel to the surface of its table, screw means formoving said members and the grid plates longitudinally equally andsimultaneously and longitudinally relative to one another, and reflectorelements for viewing steroscopically photographs on the tables.ARCHIBALD BARR.

equally and simultaneously and longitud1- nally relative to one another,and reflector elements for viewing stereoscopically photographs on thetables.

2. A topographical stereoscope comprising a base plate having a straightfront edge, two tables on the base plate. each rotatable in its ownplane, two members hinged to the base plate, two grid plates, one foreach table, hinged to the two members, one to each member, the axes ofhinging of the two members and of the two grid plates being parallelwith the front edge of the base plate, and par- -ical means for movingsaid grid plates longitudinally equally and simultaneously and

